intermediate changes on #39
list function now supports --json, refs #39
made show function json serializable, added JSONSerializable mix-in to inventory.py, refs #39
adding json support for list, show, add, refs #39
merged latest model tweaks from master, refs #39
added --json support for more functions, might not have tested every combination correctly but still, closes #39
removed json output for delete, refs #39
Merge pull request #52 from gwu-libraries/t39-optional-json-output

T39 optional json output